Calcium carbonate to increase viscosity of polyacrylamide fluids

ABSTRACT

Compositions and methods of treating a subterranean formation including forming a fluid comprising polyacrylamide and calcium carbonate and introducing the fluid to the formation, wherein the viscosity of the fluid is higher than if no calcium carbonate is present. Compositions and methods of treating a subterranean formation penetrated by a well bore including forming a fluid comprising polyacrylamide, calcium carbonate, and crosslinker, and introducing the fluid to the formation, wherein the fluid viscosity at 100 s-1 is increased from 300 cP to 600 cP at a temperature of 93 degC. Compositions and methods of treating a subterranean formation penetrated by a well bore including forming a fluid comprising polyacrylamide and barium carbonate and introducing the fluid to the formation, wherein the viscosity of the fluid is higher than if no barium carbonate is present.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to methods and fluids used in treating a subterranean formation. In particular, the invention relates to the preparation and use wellbore fluids and in methods of treating subterranean formations. Also in particular, the invention relates to methods to increase the viscosity of well treatment fluids.

2. Description of the Related Art

Various types of fluids are used in operations related to the development and completion of wells that penetrate subterranean formations and to the production of gaseous and liquid hydrocarbons from natural reservoirs. These operations include drilling, perforating, fracturing, modifying the permeability, or controlling the production of sand or water. The fluids employed in these operations are known as drilling fluids, completion fluids, work-over fluids, packer fluids, fracturing fluids, stimulation fluids, conformance or permeability control fluids, wellbore cleanout fluids, gravel pack fluids, consolidation fluids, and the like, and are collectively referred to herein as well treatment fluids.

Polymers are frequently used for modifying the rheology and other physical properties of well treatment fluids including viscosity, proppant suspension, and friction reduction. Ways to improve the properties of fluids comprising polymers are needed.

SUMMARY OF THE INVENTION

Embodiments of this invention relate to a method to form and use a well treatment fluid. Embodiments of this invention relate to compositions and methods of treating a subterranean formation including forming a fluid comprising polyacrylamide and calcium carbonate and introducing the fluid to the formation, wherein the viscosity of the fluid is higher than if no calcium carbonate is present. Embodiments of this invention relate to a composition and method of treating a subterranean formation penetrated by a well bore including forming a fluid comprising polyacrylamide, calcium carbonate, and crosslinker, and introducing the fluid to the formation, wherein the fluid viscosity at 100 s-1 is increased from 300 cP to 600 cP at a temperature of 93 degC. Embodiments of this invention relate to compositions and methods of treating a subterranean formation including forming a fluid comprising polyacrylamide and barium carbonate and introducing the fluid to the formation, wherein the viscosity of the fluid is higher than if no barium carbonate is present.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plot of viscosity at 93° C. as a function of time for fluids containing 0.48 weight percent poly(acrylamide-acrylate), 0.5 volume percent titanium x-linker solution, 0.2 volume percent clay stabilizer solution, and various amounts of CaCO₃ (0%, 0.018%, 0.036%, and 0.12%).

FIG. 2 is a plot of viscosity at 121° C. as a function of time for fluids containing 0.48 weight percent poly(acrylamide-acrylate), 0.5 volume percent titanium x-linker solution, 0.2 volume percent clay stabilizer solution, and various amounts of CaCO₃ (0%, 0.018%, 0.036%, and 0.12%).

FIG. 3 is a plot of viscosity at 93° C. as a function of time for fluids containing 0.48 weight percent poly(acrylamide-acrylate), 0.5 volume percent titanium x-linker solution, 0.2 volume percent clay stabilizer solution, and 0.12 weight percent CaCl₂.

DESCRIPTION OF THE INVENTION

This invention relates to methods and compositions to form and use a well treatment fluid for treating subterranean formations. In particular, the invention relates to the use of polyacrylamide to create well treatment fluids. The invention also relates to providing a increase in viscosity of a crosslinked polyacrylamide fluid by using CaCO₃ to increase fluid viscosity of x-linked polyacrylamide fluids. Other carbonate salts (such as BaCO3) will function similarly.

At the outset, it should be noted that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developer's specific goals, such as compliance with system related and business related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time consuming but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure. The description and examples are presented solely for the purpose of illustrating the preferred embodiments of the invention and should not be construed as a limitation to the scope and applicability of the invention. While the compositions of the present invention are described herein as comprising certain materials, it should be understood that the composition could optionally comprise two or more chemically different materials. In addition, the composition can also comprise some components other than the ones already cited.

In the summary of the invention and this description, each numerical value should be read once as modified by the term “about” (unless already expressly so modified), and then read again as not so modified unless otherwise indicated in context. Also, in the summary of the invention and this detailed description, it should be understood that a concentration range listed or described as being useful, suitable, or the like, is intended that any and every concentration within the range, including the end points, is to be considered as having been stated. For example, “a range of from 1 to 10” is to be read as indicating each and every possible number along the continuum between about 1 and about 10. Thus, even if specific data points within the range, or even no data points within the range, are explicitly identified or refer to only a few specific, it is to be understood that inventors appreciate and understand that any and all data points within the range are to be considered to have been specified, and that inventors have disclosed and enabled the entire range and all points within the range.

It is possible to increase the viscosity of a crosslinked polyacrylamide fluid by using CaCO₃ to increase fluid viscosity of crosslinked polyacrylamide fluids. Other carbonate salts (such as BaCO₃) will function similarly. The polyacrylamide may be any grade material that is suitable for use in the oil field. The crosslinker may be transition metal based including titanium, zirconium, and halfnium or organic species such as formaldehyde, phenylacetate activated with hexamethylenetetramine, or other similar systems. The polyacrylamide is in a concentration of 0.01% to 5% by weight. In some embodiments, the polyacrylamide may not be crosslinked at all or partially crosslinked.

The CaCO₃ is introduced as powders, crystals, granulates, particles, flakes, or fibers. In some embodiments, it must be present in a concentration of 0.001% to 1% by weight.

Other fluid components that may be used include a crosslinker such as zirconium or titanium at a concentration of 50 ppm to 5000 ppm.

The fluid is used in applications such as hydraulic fracturing, drilling, completions, fluid loss control, sand control, and water control.

The fluid will perform at temperatures such as 50 degF (10 degC) to 400 degF (204 degC) and pressures such as 500 to 20,000 psi. Some embodiments may benefit from controlling the pH at a range of 4.5 to 9.5 using an acid, base, or a buffer solution.

EXAMPLES

The following examples are presented to illustrate the preparation and properties of fluid systems, and should not be construed to limit the scope of the invention, unless otherwise expressly indicated in the appended claims. All percentages, concentrations, ratios, parts, etc. are by weight unless otherwise noted or apparent from the context of their use.

Examples are given below to illustrate the effect of CaCO₃ on x-linked polyacrylamide fluids. For all rheology experiments performed, 0.48 weight percent polymer, 0.5 volume percent titanium x-linker solution, and 0.2 volume percent clay stabilizer solution were used. When required, CaCO₃ was added and dispersed well into the fluid. The resulting fluid viscosities were measured on a Grace M5600 rheometer with typical heating time of 15 to 20 minutes to reach the test temperature.

FIG. 1 is a plot of viscosity at 93° C. as a function of time for fluids containing 0.48 weight percent poly(acrylamide-acrylate), 0.5 volume percent titanium x-linker solution, 0.2 volume percent clay stabilizer solution, and various amounts of CaCO₃ (0%, 0.018%, 0.036%, and 0.12%). FIG. 1 shows how CaCO₃ affects the fluid at 200 degF (93 degC). The fluids with CaCO₃ are apparently more viscous than the base fluid. In addition, as the amount of CaCO₃ is gradually increased, the fluid becomes more viscous. With 0.12 weight percent CaCO₃, the final fluid exhibits almost double of the viscosity compared with the base fluid. It is believed that CaCO₃ acted as a second cross-linker, resulting in additional cross-linking. At higher temperatures, such as 250 degF (121 degC), the same trend still remained.

FIG. 1 is a plot of viscosity at 121° C. as a function of time for fluids containing 0.48 weight percent poly(acrylamide-acrylate), 0.5 volume percent titanium x-linker solution, 0.2 volume percent clay stabilizer solution, and various amounts of CaCO₃ (0%, 0.018%, 0.036%, and 0.12%). FIG. 1 displays the viscosity increase in the presence of CaCO₃ at 250 degF (121 degC).

For comparison, CaCl₂ was used in place of CaCO₃ to investigate whether very soluble calcium salts would have a similar effect on the fluid.

FIG. 2 is a plot of viscosity at 93° C. as a function of time for fluids containing 0.48 weight percent poly(acrylamide-acrylate), 0.5 volume percent titanium x-linker solution, 0.2 volume percent clay stabilizer solution, and 0.12 weight percent CaCl₂.

FIG. 2 shows that, unlike CaCO₃, CaCl₂ actually reduces the fluid viscosity. So it is not beneficial to have completely soluble calcium ions in the gel. It is likely that other carbonate salts such as BaCO₃ can also result in viscosity increase and this concept may be applicable to other Ti or Zr x-linked polymer gels.

These examples show that the addition of CaCO₃ can increase fluid viscosity of x-linked polyacrylamide fluids. This behavior was observed at least at temperatures of 200 degF (93 degC) and 250 degF (121 degC).

The particular embodiments disclosed above are illustrative only, as the invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details herein shown, other than as described in the claims below. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the invention. Accordingly, the protection sought herein is as set forth in the claims below. 

1. A method of treating a subterranean formation penetrated by a well bore, comprising: forming a fluid comprising polyacrylamide and calcium carbonate; and introducing the fluid to the formation, wherein the viscosity of the fluid is higher than if no calcium carbonate is present.
 2. The method of claim 1, wherein the fluid also comprises a cross-linker.
 3. The method of claim 2, wherein the crosslinker comprises titanium, zirconium, or halfnium.
 4. The method of claim 2, wherein the crosslinker comprises formaldehyde or phenylacetate activated with hexamethylenetetramine.
 5. The method of claim 1, wherein the polyacrylamide has a molecular weight of 1 thousand to 30 million.
 6. The method of claim 1, wherein the polyacrylamide is in a concentration of 0.01 percent to 5 percent by weight.
 7. The method of claim 1, wherein the calcium carbonate is a power, crystal, granulate, flake, or fiber.
 8. The method of claim 1, wherein the calcium carbonate has a particle size of 0.01 micron to 5 mm.
 9. The method of claim 1, wherein the fluid viscosity at 100 s-1 is increased from 300 cP to 600 cP at a temperature of 93 degC.
 10. The method of claim 1, further comprising hydraulic fracturing, drilling, perforating, modifying the permeability, completions, fluid loss control, sand control, and water control.
 11. A method of treating a subterranean formation, comprising: forming a fluid comprising polyacrylamide, calcium carbonate, and crosslinker; and introducing the fluid to the formation, wherein the fluid viscosity at 100 s-1 is increased from 300 cP to 600 cP at a temperature of 93 degC.
 12. The method of claim 11, wherein the crosslinker comprises titanium, zirconium, or halfnium.
 13. The method of claim 11, wherein the crosslinker comprises formaldehyde or phenylacetate activated with hexamethylenetetramine.
 14. The method of claim 11, wherein the polyacrylamide has a molecular weight of 1 thousand to 30 million.
 15. The method of claim 11, wherein the polyacrylamide is in a concentration of 0.01 percent to 5 percent by weight.
 16. The method of claim 11, wherein the calcium carbonate is a power, crystal, granulate, flake, or fiber.
 17. The method of claim 11, wherein the calcium carbonate has a particle size of 0.01 micron to 5 mm.
 18. The method of claim 11, wherein the fluid viscosity at 100 s-1 is increased from 300 cP to 600 cP at a temperature of 93 degC.
 19. The method of claim 11, further comprising hydraulic fracturing, drilling, perforating, modifying the permeability, completions, fluid loss control, sand control, and water control.
 20. A method of treating a subterranean formation penetrated by a well bore, comprising: forming a fluid comprising polyacrylamide and barium carbonate; and introducing the fluid to the formation, wherein the viscosity of the fluid is higher than if no barium carbonate is present. 